A toner that can be favorably fixed even when heating of a fixing roller is kept at a minimal level is demanded in terms of energy saving and downsizing of an image forming apparatus. A toner having excellent low-temperature fixability is typically prepared using a binder resin having a low melting point or a low glass transition point or a releasing agent having a low melting point. However, a toner such as described above suffers from a problem that toner particles included in the toner tend to agglomerate when the toner is stored at high temperatures. In a situation in which toner particles agglomerate, the agglomerating toner particles tend to have a charge amount lower than that of other toner particles that are not agglomerating.
A toner including toner particles that have a core-shell structure may be used in order to improve low-temperature fixability, high-temperature stability and blocking resistance of the toner. For example, Patent Literature 1 describes a toner that includes toner particles in which surfaces of toner cores are each covered by a thin film containing a thermosetting component and in which the toner cores have a softening point of at least 40° C. and no greater than 150° C.